Variable-length encoder and decoder using symbol/code-word re-association of a coding table

ABSTRACT

A variable-length encoder using a code table having a symbol/code-word re-association feature, which includes a first storing portion for storing previously generated code table information, a first re-associating portion for generating re-associated code table information and re-association information indicative of the relation between a symbol and a corresponding code word from a previously generated code table information stored in the first storing portion, based on the frequency of occurrence of externally applied symbols during a predetermined time period, a delay for delaying and outputting the same symbols as those input to the first re-associating portion during the predetermined time period, a re-association information storing portion for storing the re-associated code table information and re-association information and sequentially outputting the re-association information, a variable-length encoder for receiving the symbols stored in the delay and generating and sequentially outputting code words according to the re-associated code table information stored in the re-association information storing portion, and a multiplexer which outputs the re-association information from the re-association information storing portion and the code words output from the variable-length encoder, to thereby reduce the code length of code words generated by variable-length encoding even when the frequency of occurrence of symbols used in forming a previously generated code table is different from that of the symbols applied during the predetermined time period.

This is a continuation of application Ser. No. 08/381,649 filed Jan. 31,1995 now abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a variable-length encoding/decodingsystem for video data. More particularly, it relates to avariable-length encoding/decoding system which re-associates apredetermined relation between a symbol and a code-word based on thefrequency of occurrence of symbols to be variable-length coded (VLC), tothereby increase encoding efficiency.

2. Description of the Prior Art Recently, video and audio equipmentemploying digital signal processing methods have increased, and havebeen briskly developed. Therefore, many studies have been initiatedrelating to encoding a video and audio signal into a digital signal.Since an encoded video signal requires a large amount of digital data,various methods have been suggested to compress the encoded digital dataprior to storing it on a recording medium. Among the various compressionmethods are a transform coding method, vector-quantization method,differential pulse coded modulation (DPCM), and variable-length codingmethod. Such coding methods are used to remove redundant data containedin a digital signal and, thus, reduce the total amount of transmitted orrecorded data.

The VLC method is a technique to convert symbols in the form of[run,level], obtained through discrete cosine transform (DCT),quantization and zigzag scan operations, into corresponding code wordsby using a VLC table.

FIG. 1 shows one example of a VLC table. According to the [run,level]data of the symbols shown in FIG. 1 at the right-hand side of the table,code words having different lengths are associated with the respectivesymbols. Huffman coding is a method of associating symbols and codewords based on the frequency of occurrence of the symbols. That is,Huffman coding is a data compression method in which, considering thefrequency of occurrence of a symbol, a code word having a short lengthis associated with a symbol having a high frequency of occurrence, whilea code word having a longer length is associated with a symbol having alower frequency of occurrence. A typical example of an apparatusimplementing the above method is illustrated in FIG. 2.

FIG. 2 shows a conventional variable-length encoder, and FIG. 3depicting a conventional variable-length decoder. The variable-lengthencoder of FIG. 2 comprises an encoder 1 and VLC table 2. Thevariable-length decoder of FIG. 3 comprises a decoder 3 and variablelength decode (VLD) table 4 which is the same as to VLC table 2. When asymbol is input, encoder 1 locates a code word corresponding to theinput symbol among the code words input from VLC table 2, and outputsthe corresponding code word. Decoder 3 locates a symbol corresponding tothe input code word from VLD table 4, and outputs the correspondingsymbol, to thereby restore the original symbol input to thevariable-length encoder.

However, if there is difference between the frequency of occurrence ofsymbols used in constructing VLC table 2 and the corresponding VLD table4, and that of symbols currently used in VLC coding, optimumvariable-length coding can not be achieved. In other words, if thecharacteristics of an image to be currently variable-length coded aredifferent from those of an image used when a code table is designed, apreviously generated VLC table 2 and VLD table 4 cannot be changed toaccommodate the differing characteristics. Thus, such an encoder/decoderand method do not fully accomplish the object of compressing the entireamount of data to be stored or transmitted.

SUMMARY OF THE INVENTION

Therefore, it is an object of the present invention to provide avariable-length encoder in which, even though the symbol/code-wordassociation of a previously generated code table is used, the frequencyof occurrence of the currently input symbols is measured in order tore-associate the symbols to the appropriate code words. Such are-association provides that the amount of data to be consumed isminimized even when symbols are input that have a different frequency ofoccurrence from that of symbols considered when the code table isgenerated.

Another object of the present invention is to provide a variable-lengthdecoder for restoring the original symbols represented by the code wordsobtained by variable-length coding, in which a symbol corresponding toan input code word is searched for in a previously generated decodetable according to symbol/code-word re-association control information,to thereby decode the corresponding symbol.

To accomplish the first object of the present invention, there isprovided a variable-length encoder using symbol/code-word re-associationof a code table comprising a first storing means for storing previouslygenerated code table, a first re-associating means for generatingre-associated code table and re-association information indicative ofthe relation between a symbol and a corresponding code word from thepreviously generated code table stored in the first storing means, basedon the frequency of occurrence of externally applied symbols during apredetermined time period, a delay for delaying and outputting the samesymbols as those input to the first re-associating means during thepredetermined time period, a re-association information storing meansfor storing the re-associated code table and re-association informationand sequentially outputting the re-association information,variable-length coding means for receiving the delayed symbols andgenerating the sequentially outputting code words according to there-associated code table stored in the re-association informationstoring means, and means for multiplexing and outputting there-association information from the re-association information storingmeans and outputting the code words output from the variable-lengthcoding means.

To accomplish the second object of the present invention, there isprovided a variable length decoder using symbol/code-word re-associationof a code table comprising a second storing means for storing the samecode table as that previously generated and stored in the first storingmeans, demultiplexing means for receiving data output from the means formultiplexing, dividing and outputting re-association information andcode words, a second re-association means for receiving there-association information from the demultiplexing means, re-associatinga corresponding symbol/code-word relation, and storing re-associatedcode table, and variable-length decoding means for decoding an inputcode word based on the code table information stored in the secondre-associating means to thereby generate a symbol.

BRIEF DESCRIPTION OF THE DRAWINGS

The above objects and advantages of the present invention will becomemore apparent by describing in detail a preferred embodiment thereofwith reference to the attached drawings in which:

FIG. 1 illustrates one example of a VLC table;

FIG. 2 is a block diagram of a conventional variable-length encoder;

FIG. 3 is a block diagram of a conventional variable-length decoder;

FIG. 4 is a block diagram of one embodiment of a variable-length encoderaccording to the present invention;

FIG. 5 is a diagram for explaining the re-association of a code table bya first associating circuit;

FIG. 6 is a diagram for explaining the actually transmittedre-association information; and

FIG. 7 is a block diagram of a variable-length decoder according to thepresent invention.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIG. 4 data to be variable-length encoded, that is, asymbol, is applied to a delay circuit 10 and a first re-associatingcircuit 13. The symbol input to the circuit shown in FIG. 4 is typicallycomposed of run and level [run, level] data produced by run-lengthencoding. Delay circuit 10 delays the input symbol for a predeterminedtime period and outputs the delayed symbol to encoder 11.

First re-associating circuit 13 receives the same symbol as that inputto delay circuit 10, in order to re-associate the relation ofsymbol/code-word in a code table. In particular, first re-associatingcircuit 13 performs a code table re-association operation by using thesymbols which are input during the predetermined time period. Thepredetermined time period is that time period required to gather anappropriate number of symbols for re-associating the symbols and codewords in the code table. In typical applications the predetermined timeperiod is set to correspond to one video frame or one slice. Firstre-associating circuit 13 reads out a code table from a first storingportion 14 and stores the read-out information in a built-in memory (notshown). First re-associating circuit 13 performs the code tablere-association operation by using the code table stored in the memoryand the symbols input during the predetermined time period. The codetable re-association operation is explained in detail below withreference to FIG. 5.

The left-hand column shown in FIG. 5 represents a plurality of symbolcounters. Each symbol counter corresponding to one of the respectivesymbols. The two columns shown at the right-hand side of FIG. 5indicate, in one column, code words where each code word corresponds toone of the respective symbols, and, in the other column, the length ofthe respective code words, that is, the code length. The code lengthsatisfies the relation L(N)>L(N-1)> . . . >L(2)>L(1). In other words,code word C(1) has the shortest code length, and C(N) has the longestcode length.

Prior to re-association of a code table, the symbol counters of FIG. 5are all reset to “zero” as the initial value. First re-associatingcircuit 13 recognizes the respective symbols input during thepredetermined time period. The respective symbol counter correspondingto an input symbol, counts the corresponding input symbol and stores thecounted value. When counting of the input symbols during thepredetermined time period is finished, first re-associating circuit 13performs a symbol/code-word re-association operation by re-associatingthe relationship between symbols and code words in the code table, asshown in FIG. 5. For instance, in FIG. 5 “symbol 2” has a count value of120 which is the largest among the symbols. Accordingly, “code wordC(1)”, which has the shortest length, is associated with symbol 2. Whenthe re-association of symbols and code words with respect to all of thesymbols input during the predetermined time period is finished, firstre-associating circuit 13 outputs a re-associated code table andsymbol/code-word re-association information I(n)'s to a re-associationinformation storing portion 12. Here, I(n) refers to an index of asymbol corresponding to code word C(n). For example, in FIG. 5. I(1)=2since code word C(1) is now associated with symbol 2. When there-associated code table and symbol/code-word re-association I(n) isfinished being stored in the re-association information storing portion12, re-association information storing portion 12 outputs to multiplexer15 the symbol/code-word re-association information I(n)'s in relationwith a symbol to be variable-length encoded, according to a loadingsignal applied by a controller (not shown). An encoder 11 converts therespective symbols applied from delay circuit 10 into corresponding codewords by using the re-associated code table stored in re-associationinformation storing portion 12. In the case in which encoding isfinished, code words and corresponding symbol/code-word re-associationinformation I(n)'s are applied to multiplexer 15, and the firstre-associating circuit is initialized with the previously generated codetable stored in the first storing portion. That is, the symbol countersare all reset to zero and the re-association is reset back to that ofthe previously generated code table. This refreshing preventspropagation of errors which may happen during transmission.

FIG. 6 shows the relation between the code words C(n) output fromencoder 11 and the symbol/code-word re-association information I(n)output from re-association information storing portion 12. When “codeword C(1)” is generated with respect to the first symbol, encoder 11outputs “code word C(1),” and the symbol/code-word re-associationinformation I(1) corresponding to code word C(1), provided by thereassociation information storing portion 12, is output, which is neededby the decoder. When “code word C(2)” is generated with respect to thesecond symbol, encoder 11 outputs “code word C(2)”, and in the samemanner storing portion 12 provides symbol/code-word re-associationinformation I(2) corresponding to code word C(2) which is needed by thedecoder. When “code word C(1)” is generated with respect to the thirdsymbol, encoder 11 outputs “code word C(1),” and the symbol/code-wordre-association information I(1) corresponding to code word C(1) need notbe transmitted, since it has already been transmitted and, hence, isalready specified to the decoder. In this manner, all of the symbolsused in producing the re-associated code table are encoded. In anotherembodiment of the invention, the re-association information istransmitted prior to a symbol only when the symbol is transmitted forthe first time. That is, symbol/code-word re-association information isoutput only for code words first encountered. As a result, even when asymbol is counted several times informing a re-associated code table,multiplexer 15 outputs only one set of symbol/code-word re-associationinformation with respect to that symbol. Symbol/code-word re-associationinformation with respect to those symbols that are not used in producingthe re-associated code table information, is not transmitted. Thesymbol/code-word re-association information indicative of the symbolcode-word relation used in encoding, and the corresponding code wordsgenerated by the encoder are output to multiplexer 15. Multiplexer 15multiplexes and outputs code words C(n)'s corresponding to the inputsymbols and symbol/code-word re-association information I(n)'s in such amanner that the symbol/code-word re-association information is outputfirst and then all of the code words generated are output.

The present invention can be modified in the following manner, which,however, is not applied to the embodiment described above, rather thantransmitting only one symbol/code-word re-association information I(n)with respect to multiple instances of a same symbol previouslygenerated, corresponding symbol/code-word re-association information ismultiplexed and transmitted whenever a code word corresponding to asymbol that is the same as a previously generated symbol is transmitted.

Referring to FIG. 7, which shows a variable-length decoder, a secondre-associating circuit 18 reads a previously pre-defined generated codetable from a second storing portion 19, and stores the in a memory (notshown). When the code table is stored in the memory of secondre-associating circuit 18, a demultiplexer 16 receives data output frommultiplexer 15 shown in FIG. 4, and demultiplexes and outputs the data.More specifically, demultiplexer 16 divides received data intosymbol/code word re-association information and code words.Demultiplexer 16 outputs the symbol/code-word re-association informationto second re-associating circuit 18, and outputs the code words torecorder 17. Second re-associating circuit 18 re-associates therelationship between the symbols and the code words of the code tablepreviously established according to the symbol/code-word re-associationinformation output from demultiplexer 16. The re-associated table isstored in a built-in memory (not sown). In the data output fromdemultiplexer 16, the symbol/code-word re-association information isoutput first and the corresponding code word is output later. Decoder 17outputs a symbol corresponding to the code word.

Accordingly, in the present invention, even when the frequency ofoccurrence of symbols during a predetermined time period is differentfrom that of symbols earlier used in constructing a code tale, the codelength of the code words generated by variable-length coding can bereduced. This decreases the amount of data transmitted or stored overthat stored or transmitted when the previously generated pre-definedcode table is used. Further, the present invention can efficientlytransmit information for symbol/code-word re-association to a decoder,thus, increasing the compression efficiency of data transmitted todecoders.

While the present invention has been shown and described with referenceto particular embodiments thereof, it will be understood by thoseskilled in the art that various changes in form and details may beeffected therein without departing from the spirit and scope of theinvention as defined by the following claims.

What is claimed is:
 1. A variable-length code word transmission system,comprising: encoder means for receiving and encoding input symbols intovariable-length code words based on a frequency of occurrence of saidsymbols, said encoder means including means for re-associating arelationship between code words and each distinct received symbol andgenerating re-association information for each distinct received symbol;and means for transmitting said re-association information generated bysaid means for re-associating and said variable-length code words in analternating manner; and decoder means for decoding the transmittedvariable-length code words based on said transmitted re-associationinformation.
 2. The variable-length code word transmission systemclaimed in claim 1, wherein said encoder means further comprises: faststoring means for storing a previously generated code table; firstre-associating means for receiving externally applied symbols during apredetermined time period, generating a re-associated code table andre-association information indicative of a relation between a symbol anda corresponding code word from said previously generated code tablestored in said first storing means, based on the frequency of occurrenceof the externally applied symbols during a predetermined time period;delay means for delaying and outputting the same symbols as those inputto said first re-associating means during the predetermined time period;re-association information storing means for storing said re-associatedcode table and re-association information for each distinct receivedsymbol and sequentially outputting said re-association information;variable-length coding means for receiving said symbols output from saiddelay means and generating and sequentially outputting code wordsaccording to said re-associated code table stored in said re-associationinformation storing means; and means for multiplexing and outputtingsaid re-association information from said re-association informationstoring means and said code words output from said variable-lengthcoding means.
 3. The variable-length code word transmission systemclaimed in claim 1, wherein said decoder means comprises: storing meansfor storing the same code table as that previously generated and storedin the encoder means; demultiplexing means for receiving data outputfrom the encoder means, and dividing and outputting symbol/code-wordre-association information and code words from the received data;re-associating means for receiving said re-association information fromsaid demultiplexing means, re-associating a code-word and acorresponding symbol, and storing said re-associated code table; andvariable-length decoding means for decoding said code words based onsaid code table stored in said re-associating means to thereby generatea symbol.
 4. The variable-length code word transmission system asclaimed in claim 1, wherein said encoder means is a Huffmanvariable-length encoder.
 5. The variable-length code word transmissionsystem as claimed in claim 1, wherein said decoder means is a Huffmanvariable-length decoder.
 6. The variable-length code word transmissionsystem claimed in claim 1, wherein said means for transmitting transmitssaid re-association information whenever a corresponding variable-lengthcode word is transmitted.
 7. A variable-length encoder usingsymbol/code-word re-association of a code table comprising: delay meansfor delaying externally applied symbols; first storing means for storinga previously generated code table; first re-associating means forgenerating a re-associated code table and re-association informationindicative of the relation between one of said symbols and acorresponding code word from said previously generated code table storedin said first storing means, based on a frequency of occurrence of theexternally applied symbols during a predetermined time period, whereinsaid first re-associating means generates re-association information foreach different one of the externally applied symbols; re-associationinformation storing means for storing said re-associated code table andsaid re-association information, and sequentially outputting saidre-association information; variable-length encoding means for receivingthe delayed symbols and generating and sequentially outputting codewords according to said re-associated code table stored in saidre-association information storing means; and means for multiplexing andoutputting said re-association information output from saidre-association information storing means, and said code words outputfrom said variable-length encoding means in an alternating manner. 8.The variable-length encoder using a symbol/code-word re-association of acode table as claimed in claim 7, wherein said first re-associatingmeans re-associates said symbols to said code words of said previouslygenerated code word table stored in said first storing means so that,for symbols used in re-association of the code table, a symbol having ahigher frequency of occurrence is associated with a code word having ashorter length.
 9. The variable-length encoder using symbol/code-wordre-association of a code table as claimed in claim 7, wherein said firstre-associating means comprises: a plurality of symbol counters forcounting the number of each symbol applied during the predetermined timeperiod and storing the counted values for each of the respectivesymbols, said first re-associating means generating the re-associatedcode table and re-association information from a previously generatedcode table, based on the counted values.
 10. The variable-length encoderusing symbol/code-word re-association of a code table as claimed inclaim 7, wherein said predetermined time period is a time periodrequired to re-associate symbols to code words of a code table by usingsymbols obtained from one slice of video data.
 11. The variable-lengthencoder using symbol/code-word re-association of a code table as claimedin claim 7, wherein said predetermined time period is a time periodrequired to re-associate symbols to code words of a code table by usingsymbols obtained from one frame of video data.
 12. The variable-lengthencoder using symbol/code-word re-association of a code table as claimedin claim 7, wherein said re-association information storing meansoutputs corresponding re-association information to said multiplexingmeans whenever during the predetermined interval a code word is firstoutput from said variable-length coding means.
 13. The variable-lengthencoder using symbol/code-word re-association of a code table as claimedin claim 7, wherein said re-association information storing meansoutputs only one set of re-association information to said means formultiplexing with respect to a plurality of the same code words.
 14. Thevariable-length encoder using symbol/code-word re-association of a codetable as claimed in claim 7, wherein said means for multiplexing outputsthe re-association information corresponding to a code word prior tooutputting the corresponding code word.
 15. The variable-length encoderusing symbol/code-word re-association of a code table as claimed inclaim 7, wherein said re-association information storing means outputsre-association information corresponding to each code word to saidmultiplexing means in order in which the distinnct symbols occurs. 16.The variable-length encoder using symbol/code-word re-association of acode table as claimed in claim 7, wherein said variable length encodingmeans is a Huffman encoder.
 17. The variable-length encoder usingsymbol/code-word re-association of a code table as claimed in claim 4,wherein said means for multiplexing and outputting outputs saidre-association information whenever a corresponding code word istransmitted.
 18. A variable-length decoder for decoding output from avariable-length encoder using symbol/code-word re-association of a codetable, the encoder having a previously generated code table stored in acode table, and which outputs data including code words andsymbol/code-word re-association information, the decoder comprising:storing means for storing the same code table as that previouslygenerated and stored in the variable-length encoder; demultiplexingmeans for receiving data output from the variable-length encoder, anddividing and outputting symbol/code-word re-association information andcode words from the received data, wherein the symbol/code wordre-association information for one of the code words is received onlywhen the code word is received for the first time during a predeterminedtime interval and before another code word is received; re-associatingmeans for receiving said re-association information from saiddemultiplexing means, re-associating a code-word and a correspondingsymbol, and storing said re-associated code table information; andvariable-length decoding means for decoding the code words based on saidcode table information stored in said re-associating means to therebygenerate a symbol.
 19. The variable-length decoder as claimed in claim18, wherein said re-associating means re-associates a code word and asymbol only when said code word has been received and before saidanother code word is received.
 20. The variable-length decoder fordecoding the output from a variable-length encoder usingsymbol/code-word re-association of a code table as claimed in claim 18,wherein said variable-length decoding means is a Huffman decoder. 21.The variable-length decoder for decoding the output from avariable-length encoder using symbol/code-word re-association of a codetable as claimed in claim 18, wherein said pre-determined time intervalis a time period for one slice of video data.
 22. The variable-lengthdecoder for decoding the output from a variable-length encoder usingsymbol/code-word re-association of a code table as claimed in claim 18,wherein said pre-determined time interval is a time period for one frameof video data.
 23. A variable-length decoder for decoding output from avariable-length encoder using symbol/code-word re-association of a codetable, the encoder having a previously generated code table stored in acode table, and which outputs data including code words andsymbol/code-word re-association information, the decoder comprising:storing means for storing the same code table as that previouslygenerated and stored in the variable-length encoder; demultiplexingmeans for receiving data output from the variable-length encoder, anddividing and outputting symbol/code-word re-association information andcode words from the received data, wherein said code words and saidsymbol/code-word re-association information are received in analternating manner, and symbol/code-word re-association information forany one of the code words is received before said code words arereceived; re-associating means for receiving said re-associationinformation from said demultiplexing means, re-associating a code wordand a corresponding symbol when said code word is first received, andstoring said re-associated code table information; and variable-lengthdecoding means for decoding the code word based on the code tableinformation stored in said re-associating means to thereby generate asymbol.
 24. The variable-length decoder for decoding output from avariable-length encoder using symbol/code-word re-association of a codetable as claimed in claim 23, wherein said variable-length decodingmeans is a Huffman decoder.
 25. The variable-length decoder for decodingoutput from a variable-length encoder using symbol/code-wordre-association of a code table as claimed in claim 23, wherein saiddemultiplexing means receives symbol/code-word re-associationinformation whenever a corresponding code word is received.
 26. Avariable-length encoding method, comprising: receiving input data;delaying the received input data for a pre-determined time period;counting occurrences of each distinct input data using the delayed inputdata; re-associating a relationship between code words and each distinctreceived input data based on the counted occurrence of each distinctinput data, and generating re-association information for each distinctreceived input data, wherein the code words are read from a previouslygenerated code book; encoding said received input data using there-associated relationship and outputting selected code words; andtransmitting said re-association information and the selected code wordsin an alternating manner.
 27. A variable-length encoding method asclaimed in claim 26, wherein said re-associating is carried out at apre-determined time interval.
 28. A variable-length encoding method asclaimed in claim 27, wherein said pre-determined time interval is a timeperiod for one slice of video data.
 29. A variable-length encodingmethod as claimed in claim 27, wherein said pre-determined time intervalis a time period for one frame of video data.
 30. A variable-lengthdecoding method, comprising: receiving interleaved re-associationinformation and code word data and separating said re-associationinformation and said code word data; generating a re-associated codebook by modifying association of code words and symbol data as definedin a previously generated code book using said re-associationinformation; and decoding said received code word data using saidre-associated code book and outputting decoded data.
 31. Avariable-length decoding method as claimed in claim 30, wherein saidre-association information is received only for distinct received codeword data.
 32. A variable-length decoding method as claimed in claim 30,wherein said re-association information is received for each receivedcode word data.
 33. A variable-length decoding method as claimed inclaim 30, wherein said generating a re-associated code book is carriedout at a pre-determined time interval.
 34. A variable-length decodingmethod as claimed in claim 33, wherein said pre-determined time intervalis a time period for one slice of video data.
 35. A variable-lengthdecoding method as claimed in claim 33, wherein said pre-determined timeinterval is a time period for one frame of video data.
 36. A digitaldata transmission method, comprising: receiving input data; delaying thereceived input data for a pre-determined time period; countingoccurrences of each distinct input data using the delayed input data;re-associating a relationship between code words and each distinctreceived input data based on the counted occurrence of each distinctinput data, and generating re-association information for each distinctreceived input data, wherein the code words are read from a previouslygenerated code book; encoding said received input data using there-associated relationship and outputting selected code words;transmitting said re-association information and the selected code wordsin an alternating manner; receiving the re-association information andcode word data and separating said re-association information and saidcode word data; generating a re-associated code book by modifyingassociations of code words and symbol data as defined in a previouslygenerated code book using said re-association information; and decodingsaid received code word data using said re-associated code book andoutputting decoded data.
 37. A variable-length encoding method,comprising: receiving input symbol data; adapting a relationship betweeneach distinct received input symbol data and variable-length code wordsand generating adapted association information for each distinctreceived input symbol data; generating a current code book, having adifferent association of code words and symbol data as compared to apreviously generated code book, in accordance with said adaptedassociation information; variable length coding said input symbol datainto variable length code words using said current code book to generatevariable length code words; and transmitting said adapted associationinformation and said variable length code words in an alternatingmanner.
 38. The variable-length encoding method as claimed in claim 37 ,wherein the code words of said current code book and said previouslygenerated code book are identical.
 39. The variable-length encodingmethod as claimed in claim 38 , wherein said generating a current codebook is carried out at a predetermined interval.
 40. The variable-lengthencoding method as claimed in claim 39 , wherein said predeterminedinterval is for one slice of video data.
 41. The variable-lengthencoding method as claimed in claim 39 , wherein said predeterminedinterval is for one frame of video data.
 42. The variable-lengthencoding method as claimed in claim 39 , wherein said predeterminedinterval is for one field of video data.
 43. A variable-length decodingmethod, comprising: receiving interleaved adapted associationinformation and code word data; generating a current code book, having adifferent association of code words and symbol data as compared to apreviously generated code book, in accordance with said adaptedinformation; and decoding said received code word data using saidcurrent code book and outputting decoded data.
 44. The variable-lengthdecoding method as claimed in claim 43 , wherein the code words of saidcurrent code book and said previously generated code book are identical.45. The variable-length decoding method as claimed in claim 44 , whereinsaid generating a current code book is carried out at a predeterminedinterval.
 46. The variable-length decoding method as claimed in claim 45, wherein said predetermined intervals is for one slice of video data.47. The variable-length decoding method as claimed in claim 45 , whereinsaid predetermined interval is for one frame of video data.
 48. Thevariable-length decoding method as claimed in claim 45 , wherein saidpredetermined interval is for one field of video data.
 49. Avariable-length decoding method, comprising: receiving interleavedadapted association information and code word data; generating a currentcode book, having a different association of code words and symbol dataas compared to a previously generated code book, in accordance with saidadapted association information; and decoding said received code worddata using said current code book and outputting decoded data.
 50. Thevariable-length decoding method as claimed in claim 49 , wherein thecode words of said current code book and said previously generated codebook are identical.
 51. The variable-length decoding method as claimedin claim 50 , wherein said generating a current code book is carried outat a pre-determined interval.
 52. The variable-length decoding method asclaimed in claim 51 , wherein said predetermined interval is for oneslice of video data.
 53. The variable-length decoding method as claimedin claim 51 , wherein said predetermined interval is for one frame ofvideo data.
 54. The variable-length decoding method as claimed in claim51 , wherein said predetermined interval is for one field of video data.55. A variable-length encoding method, comprising: receiving inputsymbol data; adapting a relationship between each distinct receivedinput symbol data and variable-length code words and generating adaptedassociation information for each distinct received input symbol data,wherein the adapted association information for a code word is receivedonly when the code word data is received for the first time during apredetermined time interval and before another code word data isreceived; encoding said received input symbol data using a current codebook, having a different association of code words and symbol data ascompared to a previously used code book, in accordance with said adaptedassociation information, to generate variable length code words; andtransmitting said adapted association information and said variablelength code words in an alternating manner.
 56. The variable-lengthencoding method as claimed in claim 55 , wherein the code words of saidcurrent code book and said previously used code book are identical. 57.The variable-length encoding method as claimed in claim 56 , whereinsaid encoding said received input symbol data using said current codebook is carried out at a pre-determined interval.
 58. Thevariable-length encoding method as claimed in claim 57 , wherein saidpredetermined interval is for one slice of video data.
 59. Thevariable-length encoding method as claimed in claim 57 , wherein saidpredetermined interval is for one frame of video data.
 60. Thevariable-length encoding method as claimed in claim 57 , wherein saidpredetermined interval is for one field of video data.
 61. Avariable-length decoding method, comprising: receiving interleavedadapted association information and code word data; decoding saidreceived code word using a code book, having a different association ofcode words and symbol data as compared to a previously used code book,in accordance with said adapted association indication information; andoutputting said decoded code word data.
 62. The variable-length decodingmethod as claimed in claim 61 , wherein the code words of said currentcode book and said previously used code book are identical.
 63. Thevariable-length decoding method as claimed in claim 62 , wherein saiddecoding said received code words comprises generating a current codebook based on said adapted indication information during apre-determined interval.
 64. The variable-length decoding method asclaimed in claim 63 , wherein said predetermined interval is for oneslice of video data.
 65. The variable-length decoding method as claimedin claim 63 , wherein said predetermined interval is for one frame ofvideo data.
 66. The variable-length decoding method as claimed in claim63 , wherein said predetermined interval is for one field of video data.